Feb 10, 2013

Most sudden deaths in Malaysia are caused by cardiovascular
diseases, disorders of the heart and blood vessels. The tendency
to develop cardiovascular disease is inherited to some extent, but lifestyle
plays a large role, too. Nongenetic factors that increase the risk of
cardiovascular problems include smoking, lack of exercise, a diet rich in
animal fat, and high concentrations of cholesterol in the blood.

Cholesterol travels in the blood plasma mainly in the form
of particles consisting of thousands of cholesterol molecules and other lipids
bound to a protein. One type of particle—low–density lipoproteins (LDLs), often called
the “bad cholesterol”—is associated with the deposition of cholesterol in
arterial plaques, growths that develop on the inner walls of arteries. Another
type—high–density
lipoproteins (HDLs), or “good cholesterol”—appears to reduce the
deposition of cholesterol. Exercise increases HDL concentration, whereas
smoking has the opposite effect on the LDL/HDL ratio.

Healthy arteries have smooth inner linings that promote
unimpeded blood flow. The deposition of cholesterol thickens and roughens this
smooth lining. A plaque forms at the site and becomes infiltrated with fibrous
connective tissue and still more cholesterol. Such plaques narrow the bore of
the artery, leading to a chronic cardiovascular disease known as atherosclerosis.

The rough lining of
an atherosclerotic artery seems to encourage the adhesion of platelets,
triggering the clotting process and interfering with circulation.

Hypertension
(high blood pressure) promotes atherosclerosis and increases the risk of heart
attack and stroke. Atherosclerosis tends to raise blood pressure by narrowing
the vessels and reducing their elasticity. According to one hypothesis, chronic
high blood pressure damages the endothelium that lines arteries, promoting
plaque formation. Fortunately, hypertension is simple to diagnose and can
usually be controlled by diet, exercise, medication, or a combination of these.
A diastolic pressure above 90 may be cause for concern, and living with extreme
hypertension—say, 200/120—is courting disaster.

As atherosclerosis progresses, arteries become narrower,
and the threat of heart attack or stroke increases. There may be warning signs.
For example, if a coronary artery is only partially blocked, the person may
feel occasional chest pain, a condition known as angina pectoris. The pain is
most likely to appear when the heart is laboring hard as a result of physical
or emotional stress, and it signals that part of the heart is not receiving
enough O2. However, many people with atherosclerosis are completely
unaware of their condition until catastrophe strikes.

The final blow is usually a heart attack or a stroke. A heart attack is
the death of cardiac muscle tissue resulting from prolonged blockage of one or
more coronary arteries, the vessels that supply oxygen–rich blood to the heart.
Because they are small in diameter to begin with, the coronary arteries are
particularly vulnerable. Such blockage can destroy cardiac muscle quickly,
since the constantly beating heart muscle cannot survive long without oxygen. A
stroke is the
death of nervous tissue in the brain, usually resulting from rupture or
blockage of arteries in the head.

Heart attacks and strokes frequently result from a
thrombus, or blood clot, that clogs an artery. A key process leading to the
clogging of an artery by a thrombus is an inflammatory response triggered by
the accumulation of LDLs in the artery′s inner lining. Such an inflammation,
which is analogous to the body′s response to a cut infected by bacteria, can cause plaques to rupture, releasing fragments that form a
thrombus. The thrombus may originate in a coronary artery or an artery in the
brain, or it may develop elsewhere in the circulatory system and reach the
heart or brain via the bloodstream. The transported clot, called an embolus, is
swept along until it lodges in an artery too small for the clot to pass. An
embolus is more likely to become trapped in a vessel that has been narrowed by
plaques. The embolus blocks blood flow, and cardiac or brain tissue downstream
from the obstruction may die from O2 deprivation. If damage in the
heart interrupts the conduction of electrical impulses through cardiac muscle,
heart rate may change drastically or the heart may stop beating altogether.
Still, the victim may survive if a heartbeat is restored by cardiopulmonary
resuscitation (CPR) or some other emergency procedure within a few minutes of
the attack. The effects of a stroke and the individual′s chance of survival
depend on the extent and location of the damaged brain tissue.